The invention relates to a brake actuating device that is intended for a vehicle and, more particularly, to a brake actuating device for a motor vehicle having a brake pedal lever, which is to be operated by the driver and which is connected in a force-conducting manner to a brake cylinder in order to actuate a piston which is arranged in the brake cylinder. An actuator is functionally connected between the piston and the brake pedal lever. The actuator is capable of varying the path length of the force-conducting connection between the brake pedal lever and the piston of the brake cylinder by way of a displaceable element. Furthermore, a spring element is provided whose spring force, which acts on the brake pedal lever, varies during the variation of the path length of the force-conducting connection between the brake pedal lever and the piston of the brake cylinder by way of the actuator such that the sum of the spring force and the force, which acts on the brake pedal lever from the brake cylinder, remains essentially unchanged. Such a brake actuating device is shown in DE 10 2005 036 922 A1, the specification of which is expressly incorporated by reference herein.
As described in DE 10 2005 036 922 A1, such a brake actuating device is advantageous especially for so-called hybrid vehicles, in which an actuation of the brake pedal lever is supposed to result in the individual case exclusively or partially in a recuperative braking of the vehicle by use of its electric drive motor, whereas the vehicle wheel brakes, which are actuated by the brake cylinder, are not supposed to be actuated at all or only to a limited degree.
FIG. 5 of DE 10 2005 036 922 A1 shows an embodiment with a so-called pedal force/spring force compensation. That is, basically in this embodiment the driver cannot feel at the brake pedal lever each intervention of the actuator, with which, for example, any pressure buildup in the brake cylinder can be prevented when the driver operates the brake pedal lever or with which a pressure buildup in the brake cylinder can be initiated without the driver having to operate the brake pedal lever. In this case the force effect of the brake cylinder, or rather of its piston on the brake pedal lever, is essentially eliminated by the force effect of a suitable compensation spring device, which also acts on the brake pedal lever.
In principle, a brake actuating device having such a pedal force/spring force compensation is advantageous, but the design (FIG. 5) depicted in DE 10 2005 036 922 A1 is relatively complex, for which reason the present invention provides a correspondingly simpler embodiment of such a brake actuating device.
The solution to this problem is characterized in that the spring element is fastened with one end directly or indirectly to the displaceable element and with the other end ultimately to the brake pedal lever with the interposition of a tensioning mechanism, which is guided by a cam track provided on the brake pedal lever. The cam track, which can be pivoted together with the brake pedal lever, and the spring element are designed such that an actuator induced displacement of the displaceable element into essentially any possible position of the brake pedal lever for the purpose of shortening the path length of the force-conducting connection between the brake pedal lever and the piston of the brake cylinder does not generate a change in the pedal force at the brake pedal lever that is perceptible to the driver.
It was recognized that the main application for the known brake actuating lies in the reduction of the path length of the so-called force-conducting connection between the brake pedal lever and the piston of the brake cylinder. That is, in a vehicle, which exhibits, besides the customary hydraulic brake system acting on the vehicle wheels, an additional so-called recuperation brake preferably in the form of an electric generator, it is possible to implement the braking request, specified by the driver of the vehicle with the brake pedal lever, at least proportionally in the recuperation brake by suitably reducing the braking request that is transmitted from the brake pedal lever to the brake cylinder, or rather its piston. Then, the actuator is actuated in a corresponding manner by an electronic control unit, which simultaneously actuates in a corresponding manner the recuperation brake. This is done especially to the effect that the element, which can be displaced by the actuator, reduces the path length of the force-conducting connection between the brake pedal lever and the piston of the brake cylinder to the degree that the braking request, specified by the driver with the brake pedal lever, is implemented in the recuperation brake. However, the invention provides that at the same time the driver shall continue to perceive the customary complete pedal force at the brake pedal lever that he would have also have perceived if his braking request had been completely transmitted to the brake cylinder.
For the application described in the preceding paragraph, the invention provides a brake actuating device that is now designed so as to be significantly simpler than that of the prior art. Instead of the known embodiment with two compensation springs, the present invention requires only one single spring element preferably in the form of a helical tension spring, which is clamped directly between the relevant components—that is, between an element, which is moved by the actuator and which produces the change in the force-conducting connection between the brake pedal lever and the brake cylinder piston, and the brake pedal lever itself.
In order to make it possible for this spring element to be able to compensate for the force, acting on the brake pedal lever from the piston of the brake cylinder, in any possible position of the brake pedal lever, which can be pivoted about a so-called support bearing, which describes a pivot axis, the active lever arm, by which this spring element engages with the brake pedal lever with respect to its pivot axis, is variable. That is, this lever arm is supposed to change in connection with a pivot motion of the brake pedal lever. The latter feature is easy to implement by way of a cam track, which can be pivoted together with the brake pedal lever and on which a tensioning mechanism is guided. This tensioning mechanism connects the end of the spring element that faces away from the moveable element of the actuator to an attachment point on the brake pedal lever. Then, the respective point at which the tensioning mechanism rests against this cam track constitutes the respective support point and, as a result, defines the lever arm with respect to the pivot axis of the brake pedal lever.
An embodiment that is especially advantageous in the above sense because it is compact is produced when the cam track is provided in the region of the support bearing of the brake pedal lever such that, when viewed in the direction of the pivot axis formed by the support bearing and being a part of the brake pedal lever, the tensioning mechanism is guided on the cam track partially around this pivot axis at a distance from the pivot axis. In this case the cam track can be provided on a stand-alone control element or the like, which is connected to the brake pedal lever. However, in an especially simple design the cam track can be incorporated into the brake pedal lever.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.